Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for requesting transmission of synchronization signals in a wireless communication system.
Related Art
3rd generation partnership project (3GPP) long-term evolution (LTE) is a technology for enabling high-speed packet communications. Many schemes have been proposed for the LTE objective including those that aim to reduce user and provider costs, improve service quality, and expand and improve coverage and system capacity. The 3GPP LTE requires reduced cost per bit, increased service availability, flexible use of a frequency band, a simple structure, an open interface, and adequate power consumption of a terminal as an upper-level requirement.
In the future versions of the LTE-A, it has been considered to configure low-cost/low-end (or, low-complexity) user equipments (UEs) focusing on the data communication, such as meter reading, water level measurement, use of security camera, vending machine inventory report, etc. For convenience, these UEs may be called machine type communication (MTC) UEs. Since MTC UEs have small amount of transmission data and have occasional uplink data transmission/downlink data reception, it is efficient to reduce the cost and battery consumption of the UE according to a low data rate.
It is expected that machine type communication (MTC) UEs are installed rather coverage-limited area such as basement. To enhance the coverage enhancement while reducing the cost of MTC UEs, it may be assumed that the network handles both normal UEs (category 1-9 UE without any additions for coverage enhancement techniques and low cost UEs (category 0 UE or new category UE without any additions for coverage enhancement techniques)), and coverage limiting UEs which are operated with coverage enhancement techniques applied. To avoid the unnecessary spectral efficiency degradation to handle coverage-limiting UEs, it is essential to best estimate the required coverage enhancement. Also, handling this new type of UEs should not jeopardize the legacy UEs which are not aware of the existence of coverage limiting UEs.
A method for reducing power for MTC UEs may be required.